There are two ways of getting the GL bank account onto a cash payment. The first way is exactly what you found, where a Control Account Set is chosen on the Payment entry, and the GL bank account is read from the Control Account. The default Control Account is defined on the customer.

The other way is to delete the value in the Control Account field on Payment entry, If you do this, then the GL Bank Account field below becomes active and editable. You can then select any GL account you wish to update - though of course you would want to select a proper bank account.

Whichever way works best (and safest) for you is the way to go. You might want to choose selecting Control Accounts to get the proper bank, so that you can be sure a valid bank account is always used. The other way might be prone to data entry errors that can't be undone easily after posting the batch.

Happy reading!
Regards,